The present invention relates to the recording, storage and reading of magnetic data, particularly rotatable magnetic recording media, such as thin film magnetic disks having smooth or textured surfaces and a lubricant topcoat for contact with cooperating magnetic transducer heads.
Thin film magnetic recording disks and disk drives are conventionally employed for storing large amounts of data in magnetizable form. In operation, a typical contact start/stop (CSS) method commences when a data transducing head begins to slide against the surface of the disk as the disk begins to rotate. Upon reaching a predetermined high rotational speed, the head floats in air at a predetermined distance from the surface of the disk, where it is maintained during reading and recording operations. Upon terminating operation of the disk drive, the head again begins to slide against the surface of the disk and eventually stops in contact with and pressing against the disk. Each time the head and disk assembly is driven, the sliding surface of the head repeats the cyclic operation consisting of stopping, sliding against the surface of the disk, floating in the air, sliding against the surface of the disk, and stopping.
For optimum consistency and predictability, it is necessary to maintain each transducer head as close to its associated recording surface as possible, i.e., to minimize the flying height of the head. Accordingly, a smooth recording surface is preferred, as well as a smooth opposing surface of the associated transducer head. However, if the head surface and the recording surface are too flat, the precision match of these surfaces gives rise to excessive stiction and friction during the start up and stopping phases, thereby causing wear to the head and recording surfaces, eventually leading to what is referred to as a xe2x80x9chead crash.xe2x80x9d Thus, there are competing goals of reduced head/disk friction and minimum transducer flying height.
Conventional practices for addressing these apparent competing objectives involve providing a magnetic disk with a roughened recording surface to reduce the head/disk friction by techniques generally referred to as xe2x80x9ctexturing.xe2x80x9d Conventional texturing techniques involve mechanical polishing or laser texturing the surface of a disk substrate to provide a texture thereon prior to subsequent deposition of layers, such as an underlayer, a magnetic layer, a protective overcoat, and a lubricant topcoat, wherein the textured surface on the substrate is intended to be substantially replicated in the subsequently deposited layers.
A typical longitudinal recording medium is depicted in FIG. 1 and comprises a substrate 10, typically an aluminum (Al)-alloy, such as an aluminum-magnesium (Alxe2x80x94Mg) -alloy, plated with a layer of amorphous nickel-phosphorus (NiP). Alternative substrates include glass, glass-ceramic materials and graphite. Substrate 10 typically contains sequentially deposited on each side thereof a chromium (Cr) or Cr-alloy underlayer 11, 11xe2x80x2, a cobalt (Co)-base alloy magnetic layer 12, 12xe2x80x2, a protective overcoat 13, 13xe2x80x2, typically containing carbon, and a lubricant topcoat 14, 14xe2x80x2. Cr underlayer 11, 11xe2x80x2 can be applied as a composite comprising a plurality of sub-underlayers 11A, 11Axe2x80x2. Cr underlayer 11, 11xe2x80x2, Co-base alloy magnetic layer 12, 12xe2x80x2 and protective overcoat 13, 13xe2x80x2, typically containing carbon, are usually deposited by sputtering techniques performed in an apparatus containing sequential deposition chambers. A conventional Al-alloy substrate is provided with a NiP plating, primarily to increase the hardness of the Al substrate, serving as a suitable surface to provide a texture, which is substantially reproduced on the disk surface.
In accordance with conventional practices, a lubricant topcoat is uniformly applied over the protective layer to prevent wear between the disk and head interface during drive operation. Excessive wear of the protective overcoat, typically comprising carbon, increases friction between the head and disk, thereby causing catastrophic drive failure. Excess lubricant at the head-disk interface causes high stiction between the head and disk. If stiction is excessive, the drive cannot start and catastrophic failure occurs. Accordingly, the lubricant thickness must be optimized for stiction and friction.
A significant factor in the performance of a lubricant topcoat is the amount of lubricant which tightly adheres to the magnetic recording media. The amount of adhering lubricant is described by the xe2x80x9cbonded lube ratioxe2x80x9d which is the ratio of the amount of lubricant directly bonded to the magnetic recording media vis-à-vis the total amount of originally applied lubricant. The portion of lubricant which is not tightly bound and easily removed by immersion of the recording media in a solvent is referred to as the xe2x80x9cmobile lubricantxe2x80x9d.
Another significant factor in the performance of a lubricant topcoat is the ability of the lubricant to resist decomposition over time, particularly decomposition by acid catalysis. For example, lubricants that resist catalytic cleavage by Lewis acids provide improved tribology under stress conditions.
Despite the importance of lubricity in recording media, few commercial lubricants are available that satisfy the demanding criteria of a lubricant topcoat. Typical conventional lubricants, such as perfluoroalkylpolyether fluids such as PFPE-1, PFPE-2, PFPE-3, PFPE-4, do not have optimal molecular structure and molecular conformation considered necessary for high bonded lube ratio as well as resistance to mainchain catalytic degradation and thermal stability.
The degree of direct bonding or bonded lube ratio is, in part, dependent upon the particular material employed for the protective overcoat and the molecular conformation of the lubricant in relation to the surface topography of the recording media. Desirably, the bonded lube ratio should be controllable to realize a meaningful improvement in stiction and wear performance of the resulting magnetic recording medium.
In view of the criticality of the lubricant topcoat, there is a continuing need for improved bonding of the lubricant to the magnetic recording media, particularly to a protective carbon overcoat. There is also a need for lubricants for use as topcoats in the manufacture of recording media with improved resistance to degradation and improved tribology under stress conditions.
An advantage of the present invention is stable, non-linear perfluoropolyalkylene or perfluoro polyarylene glycol lubricants of specific molecular conformations.
Another advantage of the present invention is a method of making a non-linear perfluoro polyalkylene or perfluoro polyarylene lubricants of specific molecular conformations.
A further advantage of the present invention is a magnetic recording medium comprising a lubricant topcoat bonded thereto at a high bonded lube ratio, wherein the lubricant comprises a stable, non-linear perfluoro polyalkylene or perfluoro polyarylene glycol of specific molecular conformation.
A still further object of the present invention is a method of manufacturing a magnetic recording medium comprising a lubricant topcoat having a high bonded lube ratio, wherein the lubricant comprises a stable, non-linear perfluoro polyalkylene or perfluoro polyarylene glycol of specific molecular conformation.
Additional objects, advantages and other features of the invention will be set forth in part in the description which follows and in part will become apparent to those having ordinary skill in the art upon examination of the following or may be learned from the practice of the invention. The objects and advantages of the invention may be realized and obtained as particularly pointed out in the appended claims.
According to the present invention, the foregoing and other objects are achieved in part by a magnetic recording medium comprising a lubricant topcoat, wherein the lubricant is a non-linear perfluoro polyalkylene or perfluoro polyarylene glycol of specific molecular conformation.
Another aspect of the present invention is lubricants comprising non-linear perfluoro polyalkylene. or perfluoro polyarylene glycols of specific molecular conformations and having the formula:
CFxxe2x80x94[xe2x80x94(xe2x80x94ROxe2x80x94)nxe2x80x94CF3]4xe2x88x92x,
wherein:
R is a C1-C10 linear or branched, substituted or unsubstituted fluoroalkyl or perfluoroalkyl group, or a substituted or unsubstituted fluoroaryl or perfluoroaryl group; x is an integer from 0 to 2; and n is a number between about 1 and about 20.
A further aspect of the present invention is a method of producing non-linear perfluoro polyalkylene or perfluoro polyarylene glycol lubricants of specific molecular conformations, which method comprises the steps of:
(a) providing a non-linear polyalkylene or polyarylene compound selected from compounds having the formula:
CHxxe2x80x94[xe2x80x94(Rxe2x80x2Oxe2x80x94)nxe2x80x94CH3]4xe2x88x92x,
xe2x80x83wherein:
Rxe2x80x2 is a C1-C10 linear or branched, substituted or unsubstituted alkyl group, or a substituted or unsubstituted aryl group; x is an integer from 0 to 2; n is a number between about 1 to about 20; and
(b) reacting the polyalkylene or polyarylene compound with a sufficient amount of fluorine under conditions and for a time sufficient to fluorinate same to form a non-linear perfluoro polyalkylene or perfluoro polyarylene glycol lubricant compound having the formula:
CFxxe2x80x94[xe2x80x94(xe2x80x94RO)nxe2x80x94CF3]4xe2x88x92x,
xe2x80x83wherein:
R is a C1-C10 linear or branched, substituted or unsubstituted fluoroalkyl or perfluoroalkyl group, or a substituted or unsubstituted fluoroaryl or perfluoroaryl group; x is an integer from 0 to 2; and n is a number between about 1 to about 20.
A still further aspect of the present invention is a method of manufacturing a magnetic recording medium, which method comprises depositing a magnetic layer on a substrate and then applying a solution of a lubricant to the surface of the magnetic layer or a protective overcoat thereon to form a lubricant topcoat, wherein the lubricant comprises a non-linear perfluoropolyalkylene or perfluoro polyarylene glycol of specific molecular conformation and having the formula:
CFxxe2x80x94[xe2x80x94(xe2x80x94ROxe2x80x94)nxe2x80x94CF3]4xe2x88x92x,
wherein:
R is a C1-C10 linear or branched, substituted or unsubstituted fluoroalkyl or perfluoroalkyl group, or a substituted or unsubstituted fluoroaryl or perfluoroaryl group; x is an integer from 0 to 2; and n is a number between about 1 to about 20.